Precision fiber optic alignment and attachment apparatus

ABSTRACT

A groove assembly for holding at least one fiber optic. The assembly includes a base, a cover and a small carrier disposed between the base and the cover. The carrier has at least one groove. At least one fiber optic is disposed in this groove and terminates at an edge surface of the carrier. The base and cover have respective edge surfaces serving as attachment surfaces for attachment of the assembly to a planar lightwave circuit (PLC). The PLC has at least one waveguide terminating at an edge, to which the fiber requires alignment. The base and/or cover are preferably formed from a material enabling attachment to the PLC, e.g., transparent to energy used for curing an adhesive. The carrier is formed from material enabling a substantially more precise formation of the grooves, e.g., silicon.

FIELD OF THE INVENTION

[0001] The present invention relates to fiber optics. More particularly,the present invention relates to a technique for precise alignment andattachment of fiber optics to planar lightwave circuits (PLCs).

BACKGROUND OF THE INVENTION

[0002] Fiber optic communication links employ in-line, opticalcomponents for various operations including amplification, attenuation,multiplexing, demultiplexing, etc. These components are often formedfrom planar lightwave circuits (PLCs), within which various structuresare used to perform the requisite optical signal processing operations.

[0003] PLCs are usually wafer-based modules formed using varioussilicon-based semiconductor formation techniques including growth,deposition and etching. The upper layers of PLCs usually employwaveguides (e.g., silica-on-silicon), deposited and etched, throughwhich the optical signals are transmitted. For effective use in fiberoptic systems, the PLC waveguides must be interfaced to fiber optics,which carry the optical signals to and from the PLC.

[0004] To ensure quality signal transmission to and from the PLC, thefiber optics must be precisely aligned to the PLC waveguides. Anymisalignment will result in signal insertion loss, which is highlyundesirable in optical networks because it directly impacts the distanceover which the optical signals can travel. Equally important are thetechniques used to attach the fiber optics to the PLC. Rigid attachmentis required to maintain alignment over the life of the component, andthrough various environmental conditions. The techniques chosen foralignment and attachment are highly interrelated since they will beimplemented on the same sub-assembly, and thus must be carefully, andcompatibly implemented, while keeping the costs of the sub-assembly toacceptable levels.

[0005] What is required, therefore, are improved techniques for aligningand attaching fiber optics to PLC waveguides, which are compatible andwhich can be implemented at reasonable costs.

SUMMARY OF THE INVENTION

[0006] These requirements are met, and further advantages are provided,by the present invention which in one aspect is a groove assembly forholding at least one fiber optic, and methods for its fabrication anduse. The assembly includes a base, a cover and a carrier disposedbetween the base and the cover. The carrier has at least one groove. Atleast one fiber optic is disposed in this groove, and therefore betweenthe carrier and the base or cover, and terminates at an edge surface ofthe carrier. The base and cover have respective edge surfaces serving asattachment surfaces for attachment of the groove assembly to a devicewith at least one waveguide terminating at an edge thereof, to which thefiber (or array of fibers) is to be aligned.

[0007] The base and/or cover are preferably formed from a first materialenabling attachment of the assembly to the device, e.g., a materialtransparent to energy to be directed through the material for curing anadhesive used to adhere the respective edge surfaces of the base andcover to the device. The carrier is formed from a second materialenabling a substantially more precise formation of the grooves thanwould the first material, e.g., silicon, which enables precise formationof the grooves.

[0008] The assembly is especially adapted for attachment to the edge ofa planar lightwave circuit (PLC). The PLC has at least one waveguiderunning to the edge thereof, and the assembly is attached via therespective edge surfaces of the base and cover, and respective matingsurfaces of the PLC, using an adhesive, such that the fiber optic isaligned to the waveguide. The PLC may also include a block, to form oneof the mating surfaces. This block may also be formed from a materialtransparent to energy to be directed through the material for curing theadhesive.

[0009] The combination of the small silicon carrier, between thetransparent base and cover, offers distinct advantages over priortechniques. High precision groove formation is possible in the silicon,thus improving optical performance. The small piece of silicon (5 mm vs.12 mm) decreases costs. Finally, larger, transparent base and coverpieces provide at least two adhesion points and other structuralintegrity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The subject matter which is regarded as the invention isparticularly pointed out and distinctly claimed in the concludingportion of the specification. The invention, however, both as toorganization and method of practice, together with further objects andadvantages thereof, may be best understood by reference to the followingdetailed description of the preferred embodiment(s) and the accompanyingdrawings in which:

[0011]FIG. 1 depicts a partially packaged planar lightwave circuit (PLC)in the form of an arrayed waveguide grating (AWG) having input andoutput fiber assemblies;

[0012]FIG. 2 is a side, cross-sectional view of the PLC package of FIG.1;

[0013]FIGS. 3a-b are cross-sectional views (side and end) of a first“glass” embodiment of an input or output fiber assembly;

[0014]FIGS. 3c-d are side, cross-sectional views of the first embodimentattached to a PLC;

[0015]FIGS. 4a-b are cross-sectional views (side and end) of a second“silicon” embodiment of an input or output fiber assembly;

[0016]FIGS. 4c-d are side, cross-sectional views of the secondembodiment attached to a PLC;

[0017]FIGS. 5a-b are cross-sectional views (side and end) of an input oroutput fiber assembly, mixed glass and silicon, in accordance with anaspect of the present invention;

[0018]FIGS. 5c-d are side, cross-sectional views of this assemblyattached to a PLC; and

[0019]FIG. 6 depicts, enlarged, the attachment face of a fiber assemblyin accordance with an aspect of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] With reference to FIG. 1, an exemplary planar lightwave circuit(PLC) package 10 is shown having an arrayed waveguide grating (AWG) on aPLC substrate 20 (e.g., silicon) in a package base 40. As known to thosein the art, an AWG employs an array of waveguides 22 having carefullycontrolled, differing path lengths which cause constructive phaseinterference patterns on the optical signals transmitted therein. Thistechnique is useful for multiplexing or demultiplexing optical signalspassed from the array input/focusing region 24/25 to the arrayoutput/focusing region 26/27. These waveguides run to the opposing edgesof the substrate 20, and interface with fiber optics 34/36 viaassemblies 35 and 37, respectively. As discussed in detail below, glassblocks 28 and 29 along the PLC edges facilitate attachment at thisinterface.

[0021] In the exemplary demultiplexing application shown, input fiberoptic 34 is interfaced to substrate 20 using a glass or silicon v-grooveblock assembly 35. Multiple output fibers 36 are also interfaced to thesubstrate 20 using a similar block assembly 37.

[0022] With reference now to the side, cross-sectional view of FIG. 2, aplanar heating element or heater 50 is now visible under substrate 20.The heater is used to ensure that substrate 20 is maintained at aconstant temperature (very uniformly across its surface), sincetemperature changes will cause minor structural changes in AWG signalpaths, and negatively impact its optical performance. Substrate 20 ismounted onto heater 50 using, for example, a low modulus siliconmaterial. Package lid 42 is shown in dashed lines.

[0023] Side views of the v-groove fiber assemblies 35 and 37 are alsoapparent here. These assemblies are usually assembled before theirattachment to the PLC, and their insertion into the package. Their mainfunction is the interface between the fiber optics 34/36, and opticalwaveguides running to the edges of PLC 20.

[0024] One embodiment of exemplary groove assembly 35 is depicted ingreater detail in the cross-sectional views of FIGS. 3a-b. Base 39 isshown into which v-grooves are formed, for holding the fibers 34. Inthis embodiment, glass (e.g., pyrex or quartz) is used as base 39. Oncethe v-grooves are formed, and the fibers are place into the grooves, aglass cover 38 (e.g., pyrex or quartz) is placed over the grooves torigidly hold the fibers in place. The edge face of this completedassembly is then polished in its entirety to ensure a planar surface(including clean fiber edge faces) for attachment to the PLC.

[0025] A similar side, cross-sectional view is shown in FIG. 3c, nowwith assembly 35 attached to PLC 20, along their interface 60.Attachment points 62 and 64 are shown, where an ultraviolet (UV) curableadhesive may be used to adhere the two assemblies. A glass block 28 isshown affixed to the edge of PLC 20, to provide structural integrityalong this edge, as well as an additional surface area for attachmentpoint 62. This combined edge is also polished. When attaching assembly35 to PLC 20, active techniques may be used to ensure alignment betweenthe PLC waveguides 24 running to this edge, and the fibers 34, now inassembly 35. Also, the mating surfaces are shown polished at an angle tominimize unwanted reflections (here exaggerated, but nominally +/−8degrees in practice).

[0026] Some performance considerations are evident when choosing theseattachment and alignment techniques. First, to ensure fiber placementaccuracy in the grooves of base 39, these grooves should be formedprecisely. In this exemplary glass embodiment, the grooves are usuallymachined into the upper surface of the base, to an accuracy of about+/−0.05 μm (micrometer) groove pitch tolerance. This may not be optimaltolerance, but the glass base does provide other notable advantages: itis strong yet transparent, thus allowing UV light energy transmission toattachment point 64 (represented as the dashed lines in the enlargedview of FIG. 3d) thus improving adhesion. Two main adhesion points 62and 64 are accessible by UV light energy transmitted through transparentmaterials, in this embodiment. Also, glass is much less expensive thanother alternative materials.

[0027] Another similar embodiment is shown in FIGS. 4a-d. Thearchitecture of assembly 135 is similar to that of assembly 35 discussedabove, however silicon is used as base 139 (rather than glass), but aglass cover 138 is still employed. Fibers 134 run through grooves formedinto the upper surface of base 139. All elements 28, 24 and 20 of PLCremain the same.

[0028] By using silicon as the base material, much more precise grooveformation is possible than with glass, e.g., +/−0.025 μm groove pitchtolerance, thus the fibers are aligned and coupled to the PLC waveguideswith much greater accuracy. The groove formation can be done with knownsilicon processing techniques, including deposition, masking, etching,etc. However, this amount of silicon (e.g., more than 12 mm in thelateral direction shown) leads to more expense, though somewhat offsetby the improved processing costs and yields over glass v-groovemachining (especially at high volumes). Also (as shown in FIG. 4d) thelower attachment point is lost because silicon is not transparent to UVlight, and most attachment is effected at attachment point 162 ofinterface 160. This results in the need for much greater process controlduring attachment, and may lead to adverse long-term reliabilityconcerns.

[0029] In accordance with the present invention, and with reference tothe side cross-sectional views of FIGS. 5a-b, groove assembly 235includes a small, thin “carrier” 231 disposed (e.g., using epoxy orother suitable connection technique) between cover 239 and base 235.Carrier 231 is formed from a material like silicon, which enables asubstantially more precise formation of grooves therein, than would thebase or cover materials (here e.g., glass—pyrex or quartz). Fibers areheld in their (here inverted) grooves, between the cover 239 and thecarrier 231. (Note that the terms “base” and “cover” are used broadlyand for convenience herein to connote any type of structures necessaryfor the structural and/or performance integrity of the assembliesdisclosed herein. They may be in opposite positions, or may not actuallyfunction as the terms “base” or “cover” may literally imply.) Allelements 28, 24 and 20 of PLC remain the same.

[0030] This carrier is, for example, about 750 μm thick, and about 5 mmalong its lateral dimension (i.e., much smaller than the 12 mm siliconbase of FIGS. 4a-d). Thus the groove formation precision is retained inthis embodiment, but at a more than 50% reduction in the usage ofsilicon. (It should be noted that both silicon embodiments are cheaperthan the machined glass embodiment of FIGS. 3a-d, because of processingissues.)

[0031] Because the carrier is disposed between the transparent base andcover, two attachment points 262 and 264 are provided along interface260. As shown in FIG. 5d, these attachment points are both easilyaccessed by UV light energy through their surrounding structures, thusincreasing the effectiveness and resilience of the attachment ofassembly 235 to PLC 20.

[0032] The invention is applicable to single input or output fibers, orlarge fiber arrays. The term “groove” is used broadly herein to connoteany type of cavity structure within carrier 231 suitable for holding alongitudinal fiber optic, and includes (without limitation) v-grooves,u-grooves, rectangular grooves, through-tubes, or any similarstructures.

[0033] Additional detail of one embodiment of the inventive assembly isshown in the perspective view of FIG. 6. Here, the combined, polishededge comprised of base 238, carrier 231, fiber array faces, and cover239 are shown. Particular advantages directly flow from thisarchitecture: High precision groove formation in a material likesilicon, thus improving optical performance; small piece of silicon (5mm vs. 12 mm) thus decreasing costs; maintenance of at least twoadhesion points and other structural integrity provided by the twolarger transparent pieces surrounding the carrier.

[0034] While the invention has been particularly shown and describedwith reference to preferred embodiment(s) thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the spirit and scope of theinvention.

1. A groove assembly for holding at least one fiber optic, comprising: abase; a cover; a carrier disposed between the base and the cover, havingat least one groove formed therein; and at least one fiber opticdisposed in a respective groove of the at least one groove, andtherefore between the carrier and the base or cover, and terminating atan edge surface of the carrier; wherein the base and cover haverespective edge surfaces which serve as attachment surfaces forattachment of the groove assembly to a device having at least onewaveguide terminating at an edge thereof, to which the at least onefiber is to be aligned.
 2. The assembly of claim 1, wherein the baseand/or cover are formed from a first material enabling attachment of theassembly to the device, and the carrier is formed from a second materialenabling a substantially more precise formation of the at least onegroove than would the first material.
 3. The assembly of claim 2,wherein the second material comprises silicon to enable preciseformation of the at least one groove.
 4. The assembly of claim 2,wherein the first material comprises a material transparent to energy tobe directed through the material for curing an adhesive used to adherethe respective edge surfaces of the base and cover to the device.
 5. Theassembly of claim 4, wherein the base and cover are formed from thefirst material.
 6. The assembly of claim 5, wherein the second materialcomprises silicon to enable precise formation of the at least onegroove.
 7. The assembly of claim 6, in combination with a planarlightwave circuit (PLC) as said device, wherein: the PLC has at leastone waveguide running to the edge thereof, and the PLC and the assemblyare attached via the respective edge surfaces of the base and cover, andrespective mating surfaces of the PLC, using said adhesive, such thatthe at least one fiber optic is aligned to the at least one waveguide.8. The combination of claim 7, wherein the PLC comprises a block mountedthereon and comprising one of the mating surfaces.
 9. The combination ofclaim 8, wherein the block is formed from a material transparent toenergy to be directed through the material for curing the adhesive. 10.The assembly of claim 1, in combination with a planar lightwave circuit(PLC) as said device, wherein: the PLC has at least one waveguiderunning to an edge thereof, and the PLC and the assembly are attached atthe respective edge surfaces of the base and cover, and respectivemating surfaces using an adhesive, such that the at least one fiberoptic is aligned to the at least one waveguide.
 11. The combination ofclaim 10, wherein the PLC comprises a block mounted thereon andcomprising one of the mating surfaces.
 12. The assembly of claim 1,wherein the at least one fiber optic comprises an array of fiber optics,and the at least one groove comprises an array of grooves into which thearray of fiber optics is disposed.
 13. A method for fabricating a grooveassembly for holding at least one fiber optic, comprising: providing abase and a cover; disposing a carrier between the base and the cover,the carrier having at least one groove formed therein; and disposing atleast one fiber optic in a respective groove of the at least one groove,and therefore between the carrier and the base or cover, and terminatingat an edge surface of the carrier; wherein the base and cover haverespective edge surfaces which serve as attachment surfaces forattachment of the groove assembly to a device having at least onewaveguide terminating at an edge thereof, to which the at least onefiber is to be aligned.
 14. The method of claim 13, wherein the baseand/or cover are formed from a first material enabling attachment of theassembly to the device, and the carrier is formed from a second materialenabling a substantially more precise formation of the at least onegroove than would the first material.
 15. The method of claim 14,wherein the second material comprises silicon to enable preciseformation of the at least one groove.
 16. The method of claim 14,wherein the first material comprises a material transparent to energy tobe directed through the material for curing an adhesive used to adherethe respective edge surfaces of the base and cover to the device. 17.The method of claim 16, wherein the base and cover are formed from thefirst material.
 18. The method of claim 17, wherein the second materialcomprises silicon to enable precise formation of the at least onegroove.
 19. The method of claim 18, in combination with a method forattaching the assembly to a planar lightwave circuit (PLC) as saiddevice, wherein the PLC has at least one waveguide running to the edgethereof, the method comprising: attaching the PLC and the assembly viathe respective edge surfaces of the base and cover, and respectivemating surfaces of the PLC, using said adhesive, such that the at leastone fiber optic is aligned to the at least one waveguide.
 20. Thecombination of claim 19, wherein said attaching includes: illuminatingthe respective edge surfaces of the base and cover and the respectivemating surfaces of the PLC with energy, through the base and the cover,to cure said adhesive.
 21. The combination of claim 20, wherein the PLCcomprises a block mounted thereon and comprising one of the matingsurfaces.
 22. The combination of claim 21, wherein the block is formedfrom a material transparent to energy to be directed through thematerial for curing the adhesive.
 23. The combination of claim 22,wherein said attaching includes: illuminating one of the respective edgesurfaces of the base and cover with energy, through the block, to curesaid adhesive.
 24. The method of claim 13, in combination with a methodfor attaching the assembly to a planar lightwave circuit (PLC) as saiddevice, wherein the PLC has at least one waveguide running to an edgethereof, the method comprising: attaching the PLC and the assembly atthe respective edge surfaces of the base and cover, and respectivemating surfaces using an adhesive, such that the at least one fiberoptic is aligned to the at least one waveguide.
 25. The combination ofclaim 24, wherein said attaching includes: illuminating the respectiveedge surfaces of the base and cover and the respective mating surfacesof the PLC with energy, through the base and the cover, to cure saidadhesive.
 26. The combination of claim 25, wherein the PLC comprises ablock mounted thereon and comprising one of the mating surfaces.
 27. Thecombination of claim 26, wherein said attaching includes: illuminatingone of the respective edge surfaces of the base and cover with energy,through the block, to cure said adhesive.
 28. The method of claim 13,wherein the at least one fiber optic comprises an array of fiber optics,and the at least one groove comprises an array of grooves into which thearray of fiber optics is disposed.
 29. A method for holding at least onefiber optic, for attachment to a device having at least one waveguideterminating at an edge thereof, and to which the at least one fiber isto be aligned, comprising: using a groove assembly, including a base anda cover, and a carrier between the base and the cover, the carrierhaving at least one groove formed therein; and disposing at least onefiber optic in a respective groove of the at least one groove, andtherefore between the carrier and the base or cover, and terminating atan edge surface of the carrier; wherein the base and cover haverespective edge surfaces which serve as attachment surfaces forattachment of the groove assembly to the device.
 30. The method of claim29, wherein the base and/or cover are formed from a first materialenabling attachment of the assembly to the device, and the carrier isformed from a second material enabling a substantially more preciseformation of the at least one groove than would the first material. 31.The method of claim 30, wherein the second material comprises silicon toenable precise formation of the at least one groove.
 32. The method ofclaim 30, wherein the first material comprises a material transparent toenergy to be directed through the material for curing an adhesive usedto adhere the respective edge surfaces of the base and cover to thedevice.
 33. The method of claim 32, wherein the base and cover areformed from the first material.
 34. The method of claim 33, wherein thesecond material comprises silicon to enable precise formation of the atleast one groove.
 35. The method of claim 34, in combination with amethod for aligning the assembly to a planar lightwave circuit (PLC) assaid device, wherein the PLC has the at least one waveguide running tothe edge thereof, the method comprising: attaching the PLC and theassembly via the respective edge surfaces of the base and cover, andrespective mating surfaces of the PLC, using said adhesive, such thatthe at least one fiber optic is aligned to the at least one waveguide.36. The combination of claim 35, wherein said attaching includes:illuminating the respective edge surfaces of the base and cover and therespective mating surfaces of the PLC with energy, through the base andthe cover, to cure said adhesive.
 37. The combination of claim 36,wherein the PLC comprises a block mounted thereon and comprising one ofthe mating surfaces.
 38. The combination of claim 37, wherein the blockis formed from a material transparent to energy to be directed throughthe material for curing the adhesive.
 39. The combination of claim 38,wherein said attaching includes: illuminating one of the respective edgesurfaces of the base and cover with energy, through the block, to curesaid adhesive.
 40. The method of claim 29, in combination with a methodfor aligning the assembly to a planar lightwave circuit (PLC) as saiddevice, wherein the PLC has the at least one waveguide running to anedge thereof, the method comprising: attaching the PLC and the assemblyat the respective edge surfaces of the base and cover, and respectivemating surfaces using an adhesive, such that the at least one fiberoptic is aligned to the at least one waveguide.
 41. The combination ofclaim 40, wherein said attaching includes: illuminating the respectiveedge surfaces of the base and cover and the respective mating surfacesof the PLC with energy, through the base and the cover, to cure saidadhesive.
 42. The combination of claim 41, wherein the PLC comprises ablock mounted thereon and comprising one of the mating surfaces.
 43. Thecombination of claim 42, wherein said attaching includes: illuminatingone of the respective edge surfaces of the base and cover with energy,through the block, to cure said adhesive.
 44. The method of claim 29,wherein the at least one fiber optic comprises an array of fiber optics,and the at least one groove comprises an array of grooves into which thearray of fiber optics is disposed.